The study of the role of Hydronium ion in Proton transfer essentially provides
evidence that the bulk water presence is a viable medium for proton transfer to
occur.
At least what happens in isolated amino acid molecule Geometry Optimization
starting with Zwitterions form can happen unhindered even in presence of water
even if water does not seem to be significantly faciliting what happens without its
presence?
At this juncture the question of greater concern seems to be to find ways for
proton transfer from the carboxylic acid function (of the nonionic amino acid) to
the alpha amino group in the molecule.
This requires much closely the possible specific water-amino acid interaction
within the coordinate sphere of the amino acid, and find how the bulk water
medium could further facilitate.
The main inference by the results
considered till now is that the
ZWITTERION form of the amino acid
exhibits the proton releasing tendency
of the ammonium group at provocation
of the presence of an Oxygen containing
system in the neighborhood and that in
the absence of any other molecule, the
carboxylate ion of the isolated amino
acid receives the proton readily.
This is what is most popularly known conditions
in Biological media.
Is it possible to investigate the role of water
mediation to such an extent that, the zwitterion
form becomes more stable in such a surrounding
as compared to the nonionic form?
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In the previous Sheet the situation of proton transfer with the
surrounding water molecules was illustrated.
The role of water molecule is more specifically displayed when the G.O.
is carried out with only two water molecules. Initial water disposition
influences the proton transfer pathway, though the end result is the
same structure.
There is only a very small shift in the location of surrounding pair of water molecules. In the
first disposition (top row sequence) the presence two water molecules does not alter the
intra molecular proton transfer pathway. On the other hand (lower row) small shift of the
two water molecules provides for only an intermolecular proton transfer. Carefully look for
the difference in the starting disposition of the water molecules. In both the cases above,
and below end result is the same to stae as nonionic form stabilizes. But, see the disposition
of the resulting water molecules and the orientation of the proton in amino acid.
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Additive and Non additive energy
contributions to clusters
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